In liquid detergents, particularly in liquid detergents used as a house detergent, a nonionic surfactant and/or an anionic surfactant are used as the surfactant and a builder of various types is added to increase detergency. Various types of organic or inorganic builders can be used but almost all builders have a Na salt structure.
In recent years, from the standpoint of environmental conservation, studies are aggressively being made on the use of an aminopolycarboxylic acid having excellent biodegradability, particularly an amino acid diacetic acid-type chelating agent, as the builder. Aminopolycarboxylic acids including amino acid diacetic acid chelating agents are used in the form of a synthetic reaction solution as it is on account of the cost. Therefore, in almost all cases, these are Na salts which assume strong alkalinity. For example, JP-A-10-25494 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a liquid detergent for dishes, comprising an aspartic acid diacetic acid builder, where an alkali metal salt is used. JP-A-10-36888 discloses a liquid detergent comprising an aminopolycarboxylic acid builder, where an amine salt is disclosed on the same level with an alkali metal salt and in Examples, a Na salt is used. Moreover, the maximum concentration of the surfactant in this composition is as low as 10 wt %, thus, the problem of white turbidity on the high concentration side is not solved.
The use of a builder has a problem in that the solubility or clouding point of the surfactant as the main agent decreases and thereby the compatibility is deteriorated to cause, for example, white turbidity or separation of the white turbidity into two layers with the elapse of time. In order to prevent these, a technique of diluting the liquid detergent composition with water to reduce the concentration of the surfactant or a technique of adding a solubilizing agent has been heretofore used. However, the former case of diluting the liquid detergent composition with water inevitably results in an increase in the cost of transporting the detergent and this is commercially disadvantageous. In the latter case, it is known to newly add a surfactant as a solubilizing agent or add a urea, an ether alcohol or a lower alcohol. However, the effect is not sufficiently high for obtaining a high concentration liquid detergent composition.